1. Field of the Invention
The present invention relates to trunked radio systems, and more particularly, to a method for selecting a control channel in a trunked radio system, in which a fault control channel retained by a group of radio units is changed into an arbitrary normal control channel selected among normal control channels, to continually execute a communication service.
2. Background of the Related Art
Generally, a trunked radio system is comprised of a plurality of repeaters which correspond to a plurality of control channels, a repeater control unit which controls the plurality of repeaters, and a repeater management station which monitors the repeater control unit. Each of the repeaters is operated by transmitting/receiving a control signal to/from a plurality of radio units such as a personal portable unit, a vehicle unit and so on.
FIG. 1 is a block diagram illustrating a construction of a conventional trunked radio system. In a conventional trunked radio system, there are provided a plurality of control channel repeaters 11-1, 11-2, . . . , 11-N which are connected in parallel with a repeater control unit (RCU) 10 via a common data bus 12, in which the repeater 11-N is allotted as a stand-by control channel repeater. Each of the control channel repeaters is constructed to generate a frequency in a phase locked loop manner. It is accordingly possible to select and fix all frequencies allotted in the trunked radio system. A reference numeral 13 indicates a repeater management station, and reference numerals 14, 15, . . . , and 18 each represent unit groups having radio units corresponding to the control channel repeaters 11-1 to 11-N.
In a method of the conventional control channel selection, a single stand-by control channel is additionally prepared for a predetermined number of control channels in preparation for the failure of the control channel repeaters. The stand-by control channel is normally in a stand-by state, but if failure on the control channel during operation occurs, it operates for the fault control channel.
Then, when the fault control channel is repaired, the stand-by control channel returns to the stand-by state and the repaired control channel is operated for communication service.
FIG. 2 is a block diagram illustrating another construction of a conventional trunked radio system. The construction of FIG. 2 is the same as that of FIG. 1 except for the stand-by control channel of FIG. 1. In other words, the construction of FIG. 2 does not include the stand-by control channel. In accordance with FIG. 2, each unit group has a primary control channel and a secondary control channel. For example, if the repeater 21-1 is designated as the primary control channel repeater of the unit group 24, the repeater 21-2 is designated as the secondary control channel repeater. A communication service is executed by transmitting/receiving a control signal through the primary control channel (e.g. CH1) of the unit group 24, and if the primary control channel is in a fault state, all radio units 24-1, 24-2, . . . , 24-M contained in the unit group 24 that use the primary control channel change their control channel to the secondary control channel (e.g. CH2) of the secondary control channel repeater 21-2, respectively. Then, the radio unit group 24 transmits/receives the control signal to/from the secondary control channel repeater 21-2 to continually execute the communication service in a corresponding site. A method for selecting a control channel in the conventional trunked radio system of FIG. 1 will be in detail discussed.
It is assumed that the repeater 11-1 was previously designated as transmitting the primary control channel of the radio unit group 14. When the radio unit group 14 is in a stand-by state, all of the radio units 14-1, 14-2, . . . , 14-M of the radio unit group 14 receive a forward signal transmitted from the repeater 11-1 as the primary control channel.
Since the forward signal contains a current site number which is used by the radio unit group, and information on all the control channels and repeaters which are available, the radio units 14-1, 14-2, . . . , 14-M can check their own locations with the information and store an available channel number which can be used during transmission. At this time, if the radio unit 14-1 is removed from its current site, since it does not receive the forward signal from the primary control channel repeater 11-1, the radio unit tries to roam. However, if the radio unit 14-1 does not receive the forward signal in the stand-by state while it is not removed from its current site then a failure on the primary control channel for the repeater 11-1 is generated at the radio units 14-1. If it is determined that the control channel repeater 11-1 is in a fault state, the repeater control unit 10 transmits information such as a channel number on the fault repeater, here 11-1, to the stand-by repeater 11-N, to continually execute the operation previously performed by the fault repeater 11-1.
Thereafter, the stand-by repeater 11-N operates a phase locked loop circuit contained therewithin on the basis of the information transmitted from the repeater control unit 10 and fixes its channel number to CH. 1, which is the same as the fault repeater 11-1, instead of its original channel number, CH. N. As a result, since the standby repeater 11-N executes the normal operations in place of the fault repeater 11-1, the radio units 14-1, 14-2, . . . , 14-M of the radio unit group 14, which have the fault repeater 11-1 as their primary control channel, are continually under the communication service.
Now, a method for use of the control channels in the conventional trunked radio system of FIG. 2 will be discussed in detail. FIG. 3 is a block diagram illustrating a detailed construction of the repeater control unit 20, the repeater 21-1 and the radio unit 24-1 of FIG. 2.
As shown in FIG. 3, the repeater control unit 20 is comprised of a system controller 20a, a memory 20b and a signal processing part 20c, and is connected to the repeater management station 23. The control channel repeater 21-1 includes a system controller 21-1a, a memory 21-1b, a signal processing part 21-1c and a signal transmitting/receiving part 21-1d. The signal processing part 21-1c is connected to the signal processing part 20c of the repeater control unit 20 via a data bus 22. The radio unit 24-1 is comprised of an antenna 24-1a, a signal transmitting/receiving part 24-1b, a signal processing part 24-1c, a memory 24-1d and a system controller 24-1e. The signal transmitting/receiving part 21-1d of the repeater 21-1 transmits/receives wireless signals from/to the signal transmitting/receiving part 24-1b of the radio unit 24-1. The other repeaters and radio units shown in FIG. 2 have the same construction as the above.
For instance, it is assumed that the primary control channel of the radio unit group 24 is designated as originating from the repeater 21-1 and the secondary control channel thereof is designated as originating from the repeater 21-2. When the radio unit 24-1 is in a stand-by state, the radio unit 24-1 receives the forward signal transmitted from the repeater 21-1 as the primary control channel. As previously described, since the forward signal contains the current site number and information on the channel numbers CH, CH. 1, CH. N of all control channels or repeaters which are available, the radio unit 24-1 can check its own location with the information, and store the available channel number which can be used during transmission.
If the repeater 21-1, having the primary control channel, is in a fault state, and if the radio unit 24-1 does not receive the forward signal from the repeater 21-1, the radio unit 24-1 fixes to the channel number CH. 2, which corresponds to the channel of the repeater 21-2, as the secondary control channel in lieu of its primary control channel number CH. 1, before trying to roam, and checks whether a forward signal is received from the repeater 21-2. If the secondary control channel is in a normal operation mode, since the radio unit 24-1 receives the forward signal from the repeater 21-2, the radio unit 24-1 will receive all control signals through the secondary control channel of repeater 21-2, without executing the roaming process.
In the same manner as the above, other radio unit groups 25 to 28 can communicate through their respective secondary control channels, when their primary control channels are in a fault state.
However, the above methods of the conventional trunked radio systems have the following disadvantages: first, in the construction of FIG. 1, since the stand-by control channel repeater, which is additionally disposed, is always in a stand-by state, without being used, an efficiency of the control channels is reduced. Furthermore, since the additional stand-by control channel repeater and control channel are required, a production cost of the system is accordingly increased. Moreover, in the case where two or more control channel repeaters are at a fault state or the stand-by control channel repeater is in a fault state, since the stand-by control channel repeater can not execute the operation of the additional fault control channel or channels, the performance of the system is accordingly degraded. In this case, the radio unit group which selects the fault repeater for the primary control channel can not be used until the fault repeater is repaired and replaced manually. On the other hand, in the construction of FIG. 2, in the case where both of the primary control channel repeater and the secondary control channel repeater, which are designated for the radio unit group, are in a fault state, the corresponding radio units can not be used until the fault control channel repeaters are repaired and replaced manually.